1. Field of the Invention
The invention relates to adhesives for dental prostheses, which comprise as active adhesive ingredient at least partially neutralized copolymers of acrylates or methacrylates and acrylic or methacrylic acid together with conventional vehicles.
2. Description of the Related Art
Adhesives for dental prostheses are used to adapt, or at least help to adapt, the denture to the mucous membrane of the soft palate tissue and to the gingival grooves, with a close, firm fit. The adhesive is applied to the moistened denture, which is then inserted into the mouth. The saliva wets the surface of the layer of adhesive, causing it to swell and at the same time developing the adhesive force.
Critical parameters are the adhesive force and duration of adhesion. In this context, the mechanisms responsible for the holding effect are highly complex. The viscosity of the vehicle base and, consequently, of the finished product plays an important part. Substances used as vehicle base include mineral oil (paraffin oil), vaseline (petrolatum) and waxes, which are diluted if required with polyethylene glycol or glycerol and which make up in total from about 20 to 60% of the finished product. The viscosity is determined primarily by the overall formulation; that is, by the totality of the active substances and vehicle substances in the adhesive. A large number of compositions exist, each tailored to particular uses.
Very good adhesive force is shown by those dental-prosthesis adhesives, known from numerous patents, for example EP-A 0 122 481 and EP-A 0 265 916, whose active adhesive compositions comprise copolymers of vinyl methyl ethers and maleic acid which have been partially or completely neutralized. Suitable salts in this context are alkali metal, alkaline earth metal or zinc salts.
The preparation of these copolymers, however, generally requires an organic solvent which has to be removed again at great technical expense. In spite of this expense its removal is in many cases not quantitative, so that in some cases residues of solvent remain in the end products. This is undesirable.
U.S. Pat. No. 4,542,168, moreover, discloses the use, as active adhesive substances, of crosslinked and partially neutralized polyacrylic acid together with at least one hydrophilic polymer. These adhesives for dental prostheses have the disadvantage that their adhesive force is still not entirely satisfactory and that they are likewise prepared in organic solvents which are still detectable in the product.